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Backflow Preventer Placement help

Okay,

Im going to be installing an irrigation system in my home. I am going to split a line in my basement that goes to the spigot and then to the irrigation. Would I place the backflow on the same pipe that goes to the Valves? Does it have to be above ground - or could I put it in the basement? I only need to install it right at the pipe that supplies the irrigation right? Not on the main line?

The 'simple' answer is that you need to check with your local building codes authority.

Requirements for backflow prevention vary greatyly from locality to locality. Some will be so strict as to require an specific RPZ (down to the part number), while others are so loose that any industry accepted form of backflow prevention is allowed.

The only industry standard backflow preventer you can install in a basement is a Duel Check Backflow assymbly (not to be confused with a simple double check valve, a DC Assy has the test cocks to "prove" each part of the device is working correctly). However, a DCA is considered the lowest level of protection, and some localities do not allow a DCA as a backflow preventer to an irrigation system.

The next level up in protection is Pressure Vaccum Breakers and Anti-siphon valves. Both work on similar principals, but a PVB goes before the valves and one protects them all, while an ASV comes after the valve (so each valve has to have one). The biggest caviot of these is that they must be installed 6" or 12" HIGHER in elevation than the highest spray head. Not a big deal on level ground, but if you property is sloped, your location of these is basically the top of the slope.

The highest level of protection is an RPZ. These can be installed anywhere that is impossible for the device to become submerged. You don't want to install one of these in a basement, because they release the water through an output port if conditions try to cause a backflow. So you have to allow for the possibility that enough water is going to come spewing out of this device as if you had a broken water pipe. As such, these must be installed above ground to prevent them from becoming submerged. (If the RPZ becomes submerged, it can cease to function correctly).

As for where to install it, you simply need to install it anywhere between your irrigation valves and the rest of the potable water supply. It's purpose is such that if a problem with the water supply suddenly caused back pressure that water tries to flow from your house to the water company, the water company doesn't suck the water out of your irrigation lines that could be contaminated from stuff on the lawn such as fertilizer (in its many forms).

However, for best performace of your irrigation system, you're going to usually want to install it as close to the water meter as possible (which for most home owners means at the curb outside, not inside a basement). You usually don't want to install it on a water line leading to a hose spigot because most hose spigots are supplied by only a 1/2" line. You're irrigation system is going to want a 3/4" or 1" supply line (unless you're limiting yourself to something like drip irrigation).

The only industry standard backflow preventer you can install in a basement is a Duel Check Backflow assymbly (not to be confused with a simple double check valve, a DC Assy has the test cocks to "prove" each part of the device is working correctly). However, a DCA is considered the lowest level of protection, and some localities do not allow a DCA as a backflow preventer to an irrigation system.

Sorry HooKoDoku, but you are the one that is a little confused. A Duel Check valve (DuC) is the simple, non testable device. The Double Check Valve (DCVA) is a testable backflow prevention assembly.

And if you are going to use short form names in brackets, use the correct short form name and identify which is which. You also might want to get your information correct. The Duel Check is the lowest form of backflow protection, not the Double Check.

The best thing that the OP should do is to contact his/her municipality of Water District for the list of acceptiable devices or assemblies. In some areas a Pressure Vacuum Breaker (PVB) is not an acceptable for of backflow protection because it doesn't protect against back pressure, only back siphonage, and it has to be installed at the proper height.

The only industry standard backflow preventer you can install in a basement is a Duel Check Backflow assymbly (not to be confused with a simple double check valve, a DC Assy has the test cocks to "prove" each part of the device is working correctly). However, a DCA is considered the lowest level of protection, and some localities do not allow a DCA as a backflow preventer to an irrigation system.

Sorry HooKoDoku, but you are the one that is a little confused. A Duel Check valve (DuC) is the simple, non testable device. The Double Check Valve (DCVA) is a testable backflow prevention assembly.

And if you are going to use short form names in brackets, use the correct short form name and identify which is which. You also might want to get your information correct. The Duel Check is the lowest form of backflow protection, not the Double Check.

The best thing that the OP should do is to contact his/her municipality of Water District for the list of acceptiable devices or assemblies. In some areas a Pressure Vacuum Breaker (PVB) is not an acceptable for of backflow protection because it doesn't protect against back pressure, only back siphonage, and it has to be installed at the proper height.

Mick

Mick,

My main point is that if a pair of check valves is going to be used as a backflow preventer, get the one that allows you to independantly test each check valve.

You are correct that the "Double Check" is the device with test cocks and the "Duel Check" is the device that does not.

But from a practical standpoint, the general public equates the two devices and the two terms. So if you tell someone to go buy a "Double Check", or even use the FULL PROPER NAME "Double Check Backflow Preventor", and don't specify you want the one with the test cocks, they are just as likely to wind up with a Dual Check rather than a Double Check.

After all, Dual Checks are going to be cheaper (so if they could, people are going to buy the cheaper one). If you try to research them on Wikipedia, "Dual Check" simply redirects to "Double Check"... and then because test cocks aren't even described, they are really describing a dual check (yet us the words "backflow prevention device"). If you look at the Watts web site, for a dual check (part# 7) they use the description "prevent the reverse flow of polluted water from entering into the drinking water supply"; while the description for a double check (part# 007) they use the description "prevent the backflow of contaminated water into the potable water supply" (sounds a whole lot like the same thing to me).

So pointing out the wrong use of the word "dual" verses "double" is meaningless unless you EMPHASIZE the TEST COCKS (which I ALWAYS DO when posting here about back flow prevention).

Thanks for your help - I was planning on getting a reduced pressure valve for the backflow. Thats a good point about running to the spigot - i do need a larger pipe. Could you go from a 1/2 to 3/4 pipe? would that work? sorry for all the newb questions!

Thanks for your help - I was planning on getting a reduced pressure valve for the backflow. Thats a good point about running to the spigot - i do need a larger pipe. Could you go from a 1/2 to 3/4 pipe? would that work? sorry for all the newb questions!

Generally speaking, when you're dealing with irrigation, you want to avoid the use of any 1/2 pipe.

One of the concerns about designing an irrigation system is that you don't want to violate the "speed limit". Basically, the energy of moving water is the square of it's velocity. Irrigation valves close really fast. When they do, the energy of all that moving water has to go somewhere. If the energy is too great, you get water hammer (which can damage your plumbing anywhere that the system is connected to, so you could blowout the hose to the toilet in your house from water hammer in the irrigation system). The general rule is that you want to avoid having the water flow any faster than about 5ft/sec. With a 1/2 copper pipe, that limits your system flow rate to about 3.5 gpm. Most irrigation systems are going to need flow rates on the order of 5 to 12 gpm (or higher). 3/4" copper will get you up to about 6 gpm. If you need more flow than that, you've got to increase to 1" copper (or Sch40 PVC). That will get you to 12gpm.

But from a practical standpoint, the general public equates the two devices and the two terms.

So pointing out the wrong use of the word "dual" verses "double" is meaningless unless you EMPHASIZE the TEST COCKS (which I ALWAYS DO when posting here about back flow prevention).

So, what you are saying is that even when you describe two different types of backflow assemblies/devices, you figure that the "general public" sees the same device? We are not talking to or about the general public. The OP asked a question, and you gave him a confusing and misleading answer, even if you did mention test cocks. If you send out the wrong information, and the OP, or other reader write it down to take to a store, can you

guarantee that they will also write down test cocks?

Another thing that I find alarming is that you actually believe what you see on Wikipedia.

Get the information and descriptions right, and it won't be meaningless.

I do appreciate you trying to set the record strait about any misleading information I might post.

Since your "correction", I'm just trying to point out that people like me that are outside of the circle if irrigation professionals like yourself are going to be confused about the difference in these two devices. I'm also simply trying to point out to people like yourself that fully understand these devices and all the terminology that simply using the correct termonology is NOT going to insure that the DIY people like myself are going to understand what is needed.

As far as Wikipedia, I never said I believed what is on Wikipedia. I will say that I find Wikipedia to be a good source of general information, so long as you take everything you read with a grain of salt because it is an information source created by an imperfect public. But if you will carefully reread my post, my point in bringing up Wikipedia was to use it as an example of how these two devices are very confusing to those outside of the irrigation profession.

But since it wasn't very clear the first time, I'll repeat my point a little more clearly:
The difference between these to devices is so confusing to those outside of the irrigation profession that Wikipedia points to just a single article when you attempt to look up either one on its web site. However, you and I both know that the two devices are actually very different serving very different purposes.

Since you do seem to have a detailed understanding of these two devices and there proper terminology, my I suggest that you take the time to better educate the world in this subject by 'fixing' Wikipedia and creating two seperate articles to detail the difference between these devices?